With much focus being placed on alternative energy and new solutions being developed every day, the possibility of powering passenger car with compressed air could be real. While we are likely years away from reliably powering a passenger vehicle with compressed air, it could be a viable form of alternative energy.
There is a company in France that has developed vehicles that run on compressed air, along with an infrastructure model for fueling that can be easily installed in existing gasoline stations - and in homes. Of course, the cars that I have seen are very light weight, so might not fulfill the definition of "regular". But as a proof of concept, the current technology could be installed in a typical car as a proof of concept.
A trials bike has been built round a scuba tank powered by an enginair air motor that does 140 kph & 100 km range.
If we fill the boot & old fuel tank space with GRP air cylinders - make the motor a 2 stroke with a new camshaft & pump those cylinders with a solar powered pump - we'd have free motoring. .